Energy absorbing rigid polyurethane foams, per se, have become increasingly important in various industries, particularly the automobile industry, in view of stringent regulations being enacted. Thus, there has been a relatively recent focus on energy absorbing polyurethane foam systems.
For example, U.S. Pat. No. 4,866,102 describes moldable energy absorbing rigid polyurethane foam compositions which are prepared by the reaction of a graft polymer dispersion in a polyoxyalkylene polyether polyol with an alkylene oxide adduct of toluenediamine or diaminodiphenylmethane with an organic polyisocyanate in the presence of a crosslinking agent and water with an additional blowing agent. Similarly, U.S. Pat. Nos. 4,116,893; 4,190,712; 4,212,954; and 4,282,330 also describe energy absorbing foams utilizing graft polymer dispersions. U.S. Pat. No. 4,722,946 describes the production of energy attenuating viscoelastic polyurethane elastomers and foams, comprising mixtures of linear and branched polyol intermediates, polyisocyanates, and optionally, extenders, blowing agents, and the like, in the presence of a catalyst whereby the isocyanate index is varied from about 65 to about 85.
U.S. Pat. No. 4,696,954 describes the preparation of molded polyurethane foams characterized by high impact strength and good thermal stability. U.S. Pat. No. 4,614,754 describes a high density rigid polyurethane foam which exhibits nearly constant strain with increasing stress in compression. U.S. Pat. No. 4,585,807 describes rigid polyurethane foams employing oxyalkylated ethylenediamine. SAE Article 910404, "Fundamental Studies of Polyurethane Foam for Energy Absorption in Automotive Interiors," discusses, in general, energy-absorbing polyurethane foams.
Under ever increasing governmental regulations addressing both personal safety and environmental concerns auto manufacturers have been put in a position where they must meet stringent impact requirements, maintain vehicle weight and reduce the use of materials having a detrimental effect on the environment. Energy absorbing rigid polyurethane foams have provided a partial solution in some impact performance requirement areas; e.g. energy absorbing fillers which can be used to stiffen door support frames, thus aiding in preserving the structural integrity of the passenger compartment of an automobile or as bolsters which can reduce effects of secondary collision (occupant-to-interior). However, foams exhibiting the desired impact characteristics generally utilize chlorinated fluorocarbons as the foaming or blowing agent. That fact alone reduces their desirability in light of mandates to reduce and eventually eliminate the use of CFCS. Further, attempts to substitute water into foam formulations particularly useful for energy absorption applications have been largely unsuccessful. Limited success has been had with certain narrowly defined formulations using water as a blowing agent, and containing a polymer polyol (graft polyol) as necessary elements of the invention. U.S. Pat. Nos. 4,190,712; 4,212,954; and 4,116,893 disclose formulations for flexible or viscoelastic foams.
Of the known foam formulations, few, if any, are processable over a relatively broad range wherein the resulting foams can be utilized for either recoverable or friable energy management applications.
While many energy absorbing polyurethane foam compositions are known in the art, there appears to be a need for foam compositions ranging in Index from between about 50 to about 150 which offer, among other improvements, an expanded processing range. By an expanded processing range it is meant that the foam compositions of the present invention allow for a broader range of demold times and broader mold temperature and pressure capabilities with minimal, if any, sacrifice in foam performance.